1. Field of Invention
This invention relates generally to compact disks and, more particularly, to the reflecting layer typically found on compact disk.
2. Description of the Related Art
Writable compact disks, i.e., compact disks upon which information can be written after the manufacture thereof, have been previously described in the related art. The Photo CD is an example of this type of storage medium. As illustrated ing FIG. 1, a writable compact disk has a pre-grooved plastic substrate 11, an (organic dye) recording layer 12, a (metal) reflector layer 13, and a protective (lacquer) overcoat. The conventional writable storage medium uses a thin layer of gold as the reflecting layer. The gold reflecting layer exhibits both high stability and high reflectivity. However, gold is expensive and has several undesirable features when used as a reflecting material in a storage medium. By way of specific example, the gold reflecting layer is typically fabricated by a sputtering deposition process in order to achieve high product throughput. However, the gold layer has relatively poor adhesion to the organic dye recording layer. During higher power writing processes, such as when information is being stored at greater than the normal reading speed and the laser power must be correspondingly increased, the gold layer delaminates and cracks are produced in the dye layer. (The higher power levels are used to expedite the writing period normally used to record information at the typical disk speed.) In addition, the gold reflecting layer exhibits enhanced noise at power levels typically used to record at speeds which are greater than the normal reading speeds. This phenomenon is referred to as Noise at Optimum Recording Power (NORP) and is a serious problem in writable media using dyes.
A need has therefore been felt for a reflecting layer in writable compact disk media which has high reflectivity and long term durability and which does not use a gold material.